GNU Chess lets most modern computers play a full game of chess. It has a plain terminal interface but supports visual interfaces such as X-Windows "xboard" and Windows-for-PC "winboard" as well as a full 3-dimensional wooden chess-board protocol for the Novag Chess board enabling one to be relatively free of the computer itself.

Eagle Mode is an advanced solution for a zoomable
user interface. It has a professional file
manager, file viewers and players for most of the
common file types, a chess game, a 3D mines game,
a multi-function clock and some fractal fun, all
integrated in a virtual cosmos.

BobChess is a simple online chess clock with Normal, Fischer, Simple Delay, and Bronstein modes. It runs entirely in your browser using trivial JavaScript. Everything is contained in one file, so it is possible to easily download a version to use offline.

Scid vs. PC is a powerful chess toolkit. It has extensive database and PGN file handling capabilities, and can be used to play chess on the internet (with FICS), against a computer chess opponent, or for chess grandmasters to prepare for tournament matches. Additionally, Scid vs. PC can run automated computer tournaments with chess engines playing against each other.

Chesley is a chess engine targeting Unix-like platforms and the xboard GUI. It implements a number of modern chess programming techniques, including bitboard move generation, transposition tables, etc.

Gameclock is a fairly simple application designed to track the time spent thinking by the players during a chess game. Various clock engines are available (speed chess, fisher chess, board games, or hourglass). The graphical interface is keyboard-driven and is intended to be minimal and simple. The code is made to be extensible to other game types.